Beam alignment device for plural beam tubes



Sept. 27, 1955 A. w. FRIEND BEAM ALIGNMENT DEVICE FOR PLURAL BEAM TUBES Filed July 8, 1954' I N V EN TOR. flzamr W FEM/v0 United States Patent BEAM ALIGNNIENT DEVICE FOR PLURAL BEAM TUBES Albert W. Friend, Bala-Cynwyd, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application July 8, 1954, Serial N 0. 442,099

10 Claims. (Cl. 313--70) This invention relates to electron beam tubes and more particularly to improvements in cathode-ray tubes utilizing two or more electron beams.

In cathode-ray tubes in which there is more than one electron beam-as for example in tri-color kinescopes with three electron gunsit is often necessary that the individual beams be in register with each other at the cathode-ray tube screen. To accomplish this alignment of the electron beams, i. e., the convergence of the electron beams so as to bring them into register, it is desirable to adjust the directions of the electron beams by means of externally applied magnetic fields. This has been done by the application of small permanent magnets outside the tube adjacent to the beams.

The chief difficulty in this procedure arises from the interaction between the various adjustments of the permanent magnets, since the magnetic field used to direct one beam ordinarily also acts on the other beams. This results in difiiculty both in achieving and maintaining alignment. The alignments of the beams are interdependent, and misalignment in one usually results in misalignment of the others.

It is an object of my invention to provide anelectron discharge device of the cathode ray type and employing a plurality of beams with improved means for registering said beams at the target or screen of the tube.

More specifically it is an object of my invention to provide such a tube in which substantially independent alignment of each beam can be had without any p'er- 'ceptible change in the alignment of the other beams.

My invention overcomes the above described difiiculties by providing separate magnetically shielded regions for each beam of electrons. The invention provides for magnetic shielding elements within the neck of the tube for substantially shielding each beam of electrons from the magnetic alignment 'control used for the other beams. Each shielding element has an opening, e. g., an open side, that exposes the shielded region to individual control action from outside the neck of the tube envelope. An adjustable magnet is mounted outside the tube envelope adjacent to the opening in each shielding element. Thus, the adjustable magnet, through the opening in the shielding element, exercises control action on each beam individually.

In the drawings:

Figure l is a side elevation partially in section of a three-gun, tri-color kinescope utilizing a preferred embodiment of my invention.

Figure 2 is an enlarged sectional view taken through line 22 of Figure 1.

Figure 3 shows a partial longitudinal section of the neck of a modification of the plural-beam cathode-ray tube shown in Figure 1.

p Figure 4 shows a cut-away perspective view of part of the neck of a plural-beam tube showing a single Shield paths.

2,719,242 Patented Sept. 27, 1955 Figure 5 illustrates a section taken through Figure 4 looking in the direction indicated by arrow A.

As seen in Figures 1- and 2, the tube envelope is provided wih a neck 10 within which is mounted a pluralbeam gun assembly. Three guns are normally employed. The electron guns 11, 12 produce beams 21, 22, and the third gun (not shown) produces beam 23. These beams, which pass essentially in an axial direction, converge toward a common axis in accordance with the electric potential applied to the beam-convergence anode 14 for example and register on a screen or target 15. Conventional magnetic scanning means (not shown) may be used to have the electron beams scan the target. Magnets 31, 32, and 33 outside the tube neck 10 are arranged adjacent to the electron beams 21, 22, and 23 over which alignment control is desired. These magnets may be moved so that both the intensity and the direction of the applied magnetic field may be controlled at will. The shielding elements 41, 42, and 43 isolate the magnetic field of each magnet to a single sector of the tube neck, and each electron beam is thus separately and independently controllable by the one adjacent magnet. The shielding elements 41, 42, and 43 are preferably composed of ferromagnetic material of high magnetic permeability at low field strengths. Among the materials found to be excellent for this purpose are Allegheny- Ludlum No. 4750 alloy, any of the permalloy series of alloys (such as 479 Molybdenum Permalloy), or any of the alloyscommonly known as mumet-al. The permalloy series of alloys is described at pages 139 through 141 in Ferromagnetism by R. M. Bozarth, 1951 edition, published by D. Van Nostrand Company, New York city, New York. Both the composition and the properties of mumetal are described at pages 591 and 592 in Metals Handbook, 1948 edition, published by The American Society of Metals, Cleveland, Ohio.

The shielding elements 41, 42, and 43, may be supported by a non-magnetic support 44 (copper, molybdenum, and Type 310 stainless steel have been found to be excellent materials for this purpose, but any nonmagnetic material may be used); the elements then act as separate magnetic shunts for each magnetic field. Thus each of the electron beams 21, 22, and 23, is encompassed by a shunted magnetic field. When a small magnet 31 (a permanent magnet or an electromagnet) of any desirable shape, such as a small bar magnet, is placed adjacent to one encompassed sector, its field is effectively shielded from other sectors and is retained within the encompassed sector by the adjacent shielding element 41. Thus it is only the encompassed beam 21 that is bent. Similarly, the other shielding elements 42, 43, shunt the other' respective magnetic fields, allowing for the separate and independent bending of the other beams 22, 23. By this means the individual beams may be registered at the tube screenor at any other point as desiredwith very little interaction of the various adjustments.

The neck 10 of the tube envelope may be chosen of a ferromagnetic material and the support 44 for the shielding elements 41, 42, and 43 eliminated. The shielding elements may then be supported by the ferromagnetic neck (for support and magnetic shield continuity). The shielding elements would thus be space insulated within the tube neck so as to better isolate the adjacent shielded sectors but magnetically coupled and continuous at the tube neck. The neck would then have to be provided with appropriate magnetic flux entry ports so as to admit the magnetic flux from each magnet into its respective shielded sector.

The shielding elements may be located at any desired position along the paths of the beams. As seen in Figure 3, the shielding elements 41, 42 are inserted within a beam-convergence anode 14. Here the magnetic fields from the magnets 31, 32 control the respective beams 21, 22 through such apertures 51, 52 in the beam-convergence anode. If the anode 14 is made of a non-magnetic material, apertures need not be provided. The beamconvergence anode also forms a convenient mounting device for the shielding elements 41, 42, and 43. As the beams in this arrangement are bent at a point closer to the electron guns than if they were bent outside the beamconvergence anode, the beams may be in a lower-energy state when they are closer to the electron guns. The greater distance of the shielding elements to the screen 15 also gives a greater geometrical advantage which allows more delicate alignment control to be exercised.

The use of separate shielding elements as shown in Figures 1, 2, and 3 tends to confine each of the contained magnetic fields within the boundaries of its encompassing element; the separate shielding elements are spaced from each other by non-magnetic material. Where a single, continuous shielding element is used, as is seen in Figures 4 and 5, a somewhat lesser magnetic isolation of the several encompassed regions is afforded; a small part of the magnetic field in each sector tends to flow through the shielding into adjacent sectors. However, the beam isolating action of the single, continuous element is essentially the same as that of the separate shielding elements for purposes of beam control.

In Figure 4 a shielding element 45 is shown positioned in the tube neck on the screen side of the beam-convergence anode 14. It comprises a single, tri-vaned element which isolates each of the three electron beams 21, 22, and 23 from the magnetic control means of the other of the electron beams.

The cross-section view in Figure 5 of the beam alignment device of Figure 4 shows the positioning of the single shielding element 45 with respect to the tube neck 10, the isolated electron beams, 21, 22, and 23, and external magnets 31, 32, and 33. The beam isolating action of the tri-vaned shielding element shown here is essentially the same as that of the separate shielding elements heretofore described. The magnetic fields of the three external magnets are each essentially contained in a sector of the tube neck, each field encompassing one electron beam; each encompassed beam is thus subject to alignment control by the magnet adjacent to it and is not materially influenced by magnetic fields controlling other electron beams within the same tube.

The shielding shapes which I have pictured in the accompanying drawings are by no means exhaustive of the shapes such shielding may take. Shielding may be of any similar shape, or number of parts, provided that it isolates the several electron beams from each other and at the same time exposes each electron beam to alignment control.

While the shielding device described is useful in tricolor cathode-ray tubes, it will be appreciated that the invention is equally useful in other plural-beam tubes where separate and independent alignment control of each electron beam is desirable.

I claim:

1. An electron-beam tube having a target, means for producing a plurality of electron beams directed toward said target, means for independently magnetically controlling the direction of each of said electron beams, and means for magnetically isolating each of said electron beams from the magnetic control action on the other of said electron beams.

2. An electron-beam tube having a target, means for producing a plurality of electron beams directed along a plurality of paths toward said target, individual magnetic beam control means for each beam, and beam shielding means for magnetically isolating a portion of the region allotted to the path of each of said electron beams from the magnetic control means of the other of said electron beams, said shielding means being open adjacent to the control means for its beam.

3. A cathode-ray tube comprising an evacuated envelope having a neck portion containing a plurality of electron guns for producing separate beams of electrons, and magnetic beam shielding means disposed within the said neck portion between adjacent ones of said beams, said beam shielding means having an opening between each beam and the tube neck for subjecting each of said beams of electrons to magnetic alignment control from without the tube envelope through the said shielding opening.

4. A kinescope comprising an evacuated envelope having a neck portion containing three adjacent electron guns for producing three discrete beams of electrons, three beam-isolating magnetic shielding elements within said neck between adjacent ones of said beams, each of said shielding elements having a magnetically permeable opening therein, and three adjustable magnets disposed outside said neck adjacent, respectively, to the openings in said shielding element.

5. A tri-color kinescope comprising an evacuated envelope having a neck portion containing electron gun means for producing three discrete electron beams, a single trivaned beam-isolating magnetic shielding element within the neck of said evacuated tube with the vanes extending radially outward between said beams, and three adjustable magnets outside said neck mounted adjacent to the open space between adjacent ones of the vanes of said shielding element for eifecting individual alignment of its corresponding beam.

6. A cathode-ray tube comprising an evacuated envelope having a neck portion, a plurality of adjacent electron guns mounted within the neck portion of said envelope for producing a plurality of separate beams of electrons, a beam-convergence anode mounted with the neck portion of said envelope about the path of said beams, and magnetic beam shielding mounted within the said anode and between adjacent ones of said beams, said beam shielding having an opening between each beam and the tube neck to permit said beams to be subjected to a constant magnetic field from without the tube envelope.

7. An electron discharge device having an envelope containing a target, means mounted within said envelope opposite said target for directing a converging plurality of beams toward said target along adjacent paths, means for shielding said beams from each other along a portion of the paths of said beams, magnetic control means mounted adjacent to each of said beam paths in the vicinity of said shielding means for separately and independently controlling the direction of the paths of said beams, said shielding means confining the field of said magnetic control means to its associated beam.

8. An electron discharge device having an envelope containing a target, means mounted within said envelope opposite said target for directing a converging plurality of beams toward said target along adjacent paths, means for shielding said beams from each other along a portion of the paths of said beams, magnetic control means mounted adjacent to each of said beam paths in the vicinity of said shielding means for separately and independently controlling the direction of the paths of said beams, said shielding means being open to the field of each of said magnetic control means between each of said beams and its associated magnetic control means.

9. An electron beam tube having a target, means for producing a plurality of electron beams in a path directed toward said target, means adjacent to said path for independently magnetically controlling the direction of each of said electron beams, and magnetic isolating means for magnetically isolating each of said electron beams from the magnetic control action on the other of said electron beams, said magnetic isolating means comprising a vaned shielding element within said tube and 2,719,242 5 6 having the vanes thereof joined at a common juncture line, References Cited in the file of this patent each of said vanes radially extending away from said UNITED STATES PATENTS juncture line and between two adjacent beams.

10. The tube described in claim 9 and wherein said g g i a1 r r vanes are of a ferromagnetic material. 0 2,677,779 Goodrich M ay 4 1954 

